The present invention relates to a telecommunications system having a packet-switching communications network in which at least a first subscriber is connected to a packet-switching communications network. The present invention also relates to a method for operating such a telecommunications system.
There are various types of communications networks for transmitting voice, video data and further data. Different services and features have been developed for each of these communications networks by virtue of the various ways in which these communications networks can be used. Conventional communications networks for the transmission of voice are generally circuit-switching communications networks and communications networks for transmitting other data are usually packet-switching communications networks; for example, a local computer network (Local Area Network; LAN) or the Internet. Presently, however, at present voice, data and video services of both types of communications networks can be made available. It is therefore possible, for example, to connect a subscriber to the circuit-switching communications network via a packet-switching communications network. Supplementary services such as call pick-up, three-way conferencing, large-scale conferencing, holding, displaying of toll information, closed user group, call number identification, automatic callback when busy, automatic callback when no reply, call barring, call waiting and call forwarding which are made available in known circuit-switching communications networks also can, to a certain extent, be used in packet-switching communications networks. Standards, for example in the series of Recommendations of the International Telecommunication Union Telecommunications Standardization Sector (ITU-T Recommendation) based on H.323, are defined for packet-switching communications networks. These standards include, in particular, the Standards H.323, H.225 and H.450.
An H.323 architecture for supplementary services in which there is a possibility of interaction of the services between circuit-switching and packet-switching communications networks is also known. For example, it is known that user-channel-related signaling messages for activating, deactivating, requesting and controlling services and features in the circuit-switching communications network are mapped onto signaling packets which are used in the packet-switching communications network. Preferably, “DSS1 messages”, which are defined in the ITU Standards Q.931 and Q.932, are used in the circuit-switching communications network. Preferably the standardized H.225 signaling protocol is used for transmitting the signaling packets in the packet-switching communications network; in particular, over the Internet. Service features and features which to be used require user-channel-related signaling messages are, for example, call pick-up, three-way conferencing and large-scale conferencing, holding, displaying of toll information, closed user group and call number identification services. Signaling which is independent of a user connection or a user channel is necessary for status interrogations and for activating or deactivating service features; for example, call divert, automatic callback when busy, automatic callback when no reply and call waiting.
Components such as terminals, gateways and gatekeepers are provided and defined for transmitting voice according to the H.323 Standard. Terminals are terminating devices which are connected to the packet-switching communications network. In packet-switching communications networks it is necessary for the subscriber to log on with his/her terminal. A gateway is used as an interface for converting the data protocols between the packet-switching communications network and the circuit-switching communications network. A gatekeeper is used to administer and to check user services and network capacities of a packet-switching communications network according to the H.323 Standard. The addressing of an incoming call also takes place in the gatekeeper in the packet-switching communications network. Each subscriber has an address in the packet-switching communications network. The telephone number which is selected by a calling subscriber is converted by the gatekeeper to the address of the called subscriber in the packet-switching communications network. In this way, the H.323 Standard can be used to transmit telephone calls over the Internet and in networks based on an Internet protocol.
Large packet-switching networks provide the possibility of enabling a number of employees who do not work in the same office, or do not work in the same office continuously, to use common functions via the network. This is sensible, in particular, if employees have to travel often or work as teleworkers at home. These employees are then connected to an external data network; for example, the Internet. This Internet provides these employees with access to an internal data network of the company, for example an Intranet, and to a telecommunications network of the company, e.g. the voice network. Employees who work, for example, for a department or on a project are combined into groups, which are known as CENTREX groups, in particular for the sake of better accessibility. CENTREX is a special service which is made available using a network node of a telecommunications network. CENTREX can be used to provide some of the connected subscribers, for example the employees of the department or of the project, with a range of functions corresponding approximately to the range of functions of a private branch exchange, even though they are not all connected to the same private branch exchange. Using the CENTREX service it is possible, for example, for an incoming call for one employee in the group also to be made visible and available to other preset subscribers. Thus, with the CENTREX service there is also the possibility of presetting a team call or a call transfer. Here, when there is an incoming call to a subscriber line in the group a message is generated which is transmitted to the other subscriber lines which are preset in this group. Each subscriber of the group can then receive this call. Each of the subscribers in the group can also receive calls parked in the system. The subscribers of the CENTREX group can also have a common call number schedule which can be used by all the subscriber lines. However, with the prior art, it is possible to use the CENTREX service and other services known on voice connections, such as three-way conferencing, call forwarding, call playback, subscriber cut-in, recorded announcement services and private call number schedule only in a circuit-switching communications network. According to the H.323/H.450 Standards, these services are not supported for voice connections using the packet-switching communications network, or at least not to the same extent.
An object of the present invention is, therefore, to disclose a telecommunications system having a packet-switching communications network, and a method for operating such a telecommunications system, which provides a subscriber of the packet-switching communications network with services and features of a circuit-switching communications network.